1. Field of the Invention
The present invention provides methods and reagents for DNA typing of HLA DRbeta (DRB) nucleic acids. The invention enables one to type homozygous or heterozygous samples from a variety of sources, including samples comprising RNA or cDNA templates, and to detect allelic variants not distinguishable by present serological, cellular, or biochemical methods. The present typing system facilitates typing tissue for transplantation, determining individual identity, and identifying disease susceptible individuals. The invention therefore has applications in the field of medicine generally and medical research and diagnostics specifically, the field of forensic science, and the field of molecular biology.
2. Description of Related Art
The HLA Class II proteins HLA DR, HLA DQ, and HLA DP are encoded by genes in the major histocompatibility complex (MHC) region on the short arm of human chromosome 6. The Class II proteins are heterodimeric glycoproteins consisting of an approximately 34 kD alpha chain and an approximately 29 kD beta chain. The Class II proteins are expressed on the cell surface of macrophages, B-cells, activated T-cells, and other cell types and are involved in binding and presenting antigen to helper T-lymphocytes. See the article entitled "Structure, function, and genetics of the Human Class II molecules" by Giles and Capra, 1985, Adv. Immunol. 37:1. In addition, the Class II proteins influence specific immune responsiveness by determining the repertoire of expressed T-cell receptors in mature T-lymphocytes. For a general review of the HLA Class II genes and proteins, see the article entitled "Structure, sequence and polymorphism in the HLA D region" by Trowsdale et al., 1985, Immunol. Rev. 85:5.
The Class II alpha and beta chains are encoded by separate genes, and the DP, DQ, and, DR genes are located in separate regions of the MHC. In the DR region, a single DRA locus, or gene, encodes the non-polymorphic DRalpha chain, but five different DRB loci, termed DRB1, DRB2 (now known as DRB6), DRB3, DRB4, and DRB5, encode the polymorphic DRbeta chain. Some loci are present only on certain haplotypes (such as DRB5 on the DR2 haplotype); in addition, the number of expressed DRB genes also varies between haplotypes. See the article entitled "HLA-DRbeta genes vary in number between different DR-specificities, whereas the number of DQbeta genes is constant" by Bohme et al., 1985, J. Immunol. 135:2149.
The number of distinct DRB1 alleles identified is continually increasing. The 1989 report from the WHO Nomenclature Committee for factors of the HLA system identified 34 distinct DRB1 alleles; these alleles are thought to express the serological DR specificities DR1 to DRw18. (see the article entitled "Nomenclature for factors of the HLA system, 1989" by the WHO Nomenclature Committee, 1990, Immunogenetics 31:131-140, incorporated herein by reference). By the 1990 report, the number of DRB1 alleles recognized had risen to 45 (see the article entitled "Nomenclature for factors of the HLA system, 1990" by the WHO Nomenclature Committee, 1991, Immunogenetics 33:301-309, incorporated herein by reference). The present invention provides the sequences of several newly discovered alleles.
The alleles of the DRB2 locus (now termed the DRB6 locus), which are present on DR1, DR2, and DRw10 haplotypes, are apparently not expressed. See the article entitled "Analysis of isotypic and allotypic sequence variation in the HLA DRB region using the in vitro enzymatic amplification of specific DNA segments" by Erlich et al., 1989, in Immunobiology of HLA (Dupont ed., Springer-Verlag, New York).
The alleles of the DRB3 locus, which is thought to encode the supertypic specificity DRw52 (DRw52a, DRw52b, and DRw52c), are present on the DR3, DRw6, DRw11, DRw12, DRw13, DRw14, DRw17, and DRw18 haplotypes.
The DRB4 locus, which has a single allele, encodes the DRw53 supertypic specificity and is present only on the DR4, DR7, and DRw9 haplotypes. See the article entitled "Structural relationships between the DRbeta1 and DRbeta.2 subunits in DR4, 7, and w9 haplotypes and the DRw53 (MT3) specificity" by Matsuyama et al., 1986, J. Immunol. 137:934.
The alleles of the DRB5 locus are present only on DR2 haplotypes. See the article entitled "Analysis of isotypic and allotypic sequence variation in the HLA DRB region using the in vitro enzymatic amplification of specific DNA segments," supra.
Polymorphism of the Class II DR antigens (proteins) is currently typed with allosera obtained from multiparous women in a microcytotoxicity assay on purified B lymphocytes. In addition, cellular typing protocols capable of greater specificity and based on either the specificity of alloreactive T-cell clones or the proliferative response of T-cell cultures to stimulation by homozygous typing cells (HTCs) have been developed.
These cellular-based analyses define the Dw specificities that further subdivide many of the serologically defined antigens, e.g., the five Dw subtypes of DR4. See the article entitled "Sequence polymorphism of HLA DRbeta I alleles relating to T cell recognized determinants" by Cairns et al., 1985, Nature 317:166. Both the serological and cellular assay procedures, however, are difficult and time-consuming. HLA DR DNA typing protocols based on restriction fragment length polymorphisms (RFLP) have also been developed. See U.S. Pat. No. 4,582,788, incorporated herein by reference. However, these RFLP-based analyses require large amounts of high molecular weight DNA, are labor intensive, and the limited number of informative restriction enzymes in rum limits the results obtained.
The advent of the polymerase chain reaction (PCR) has facilitated the analysis and manipulation of complex genomic DNA. The PCR process enables one to amplify a specific sequence of nucleic acid starting from a very complex mixture of nucleic acids and is more fully described in U.S. Pat. Nos. 4,683,195; 4,683,202; 4,889,818; and 4,965,188, and European Patent Publication Nos. 237,362 and 258,017, each of which is incorporated herein by reference.
The PCR process has also facilitated typing the Class II HLA DNA of an individual. Scientists have studied the polymorphic second exon of DRB loci in genomic DNA by designing oligonucleotide primers and using those primers to amplify the sequences of interest. See the article entitled "Sequence analysis of the HLA DRB and HLA DQB loci from three Pemphigus vulgaris patients" by Scharf et al., 1988, Hum. Immunol. 22:61.
When the PCR primers contain restriction enzyme recognition sequences, the amplified DNA can be cloned directly into sequencing vectors, and the nucleotide sequence of the amplification product can be readily determined. See the article entitled "Direct cloning and sequence analysis of enzymatically amplified genomic sequences" by Scharf et al., 1986, Hum. Immunol. 233:1076.
The amplified DNA can also be studied by detection methods that employ sequence-specific oligonucleotide (SSO) probes. See the article entitled "Analysis of enzymatically amplified beta-globin and HLA DQalpha DNA with allele-specific oligonucleotide probes" by Saiki et al., 1986, Nature 324:163.
Despite these advances, the complexity of the HLA DRbeta genes has prevented the development of an informative and efficient means for determining the HLA DRbeta DNA type of an individual. The present invention meets the need for an efficient, informative DRbeta DNA typing method by providing novel processes and reagents. These novel processes and reagents have in turn led to the discovery of previously unknown DRbeta alleles, which can also be typed and identified by the present method.
The present typing system can be used to type cDNA synthesized from mRNA and to type and study the expression of DRB genes in tissues, transgenic systems, disease states, and cell line. Cells that do not express the DR antigens or show unusual seroreactivity, such as tumor cells, can be readily typed. Moreover, samples from unusual sources, e.g., ancient DNAs or forensic samples, can be typed, even when the DNA sample is degraded or when only very small quantities are available for analysis.
Because PCR can amplify a fragment of target DNA over a million-fold, and because the present system can employ PCR-generated nucleic acid, radioactively labeled probes are not necessary, and nonisotopic SSOs covalently coupled to horseradish peroxidase (HRP) provide sufficient sensitivity for detection. The presence of the specifically bound HRP-labeled probes of the invention can be detected in a simple dot-blot format by chromogenic dye or chemiluminescent substrates in a matter of minutes.